For well over fifty years, there has been a need to create a flexible tube from an otherwise stiff tube by cutting the tube along the length. There are many examples of this design approach for many instruments in medical devices including catheters and guidewires (U.S. Pat. No. 5,573,520), bone reamers (U.S. Pat. Nos. 5,108,411 and 6,053,922) and other non-medical applications such flexible drill bores for well drilling (U.S. Pat. No. 2,515,365).
Flexible shafts and couplings are used to transmit rotary power between a power source and a driven part when a straight, unobstructed path is unavailable. A flexible shaft generally consists of rotating shaft with end fittings for attachment to mating parts which together construct a device. The power source is anything which can transmit the correct forces including a motor or a physician's hand. The shaft is envisioned to be used to transmit motion in a curvilinear manner such as a catheter shaft delivered through the iliac arch in the hip region, or for use as a bone reamer with flexible medullary canal reamers.
Historically, flexible shafts have been comprised of braided wire, slotted tubing, wound wire, or small diameter polymer tubing. Small diameter polymer tubing is not considered an ideal option for some applications due to a lack of pushability and high risk of kinking. This ability to transmit energy from one end of the shaft to the other is considered one of the most important characteristics when maneuvering through long, tortuous vessels. Hypotube-based shafts with a slotted or spiral cut pattern can extend the traditional limits of metal shafts, but continue to present limitations with flexibility and torque transmission. The traditional spiral cut pattern, for example, tends to wind up when torqued such that a one revolution turn at the torqued, or proximal end does not equal a one revolution turn at the non-torqued or distal end; in the worst cases, a one revolution turn results in a less than one-quarter of a revolution or less. The standard slotted pattern with no or limited male-female portion has better torqueability, but often limited bend radius along one or more planes.
Catheters and guidewires can include a full or portion of a shaft that is both flexible and torqueable or has a gradient of flexibility and torqueability along the length of the shaft. For optimal steerability and pushability, most catheter designs must have a maximum torsional rigidity while retaining a satisfactory kink-resistance and flexibility. These shafts can be used in many catheters and introducers including those for balloon angioplasty, stent delivery, electrophysiology applications, drug delivery or infusion, atherectomy, crossing catheters, or endovascular surgery. Depending on the application, the optimized and gradation of the flexibility and torqueability can be further modified by having a tube within a tube where the inside or outside tube or both can be comprised of a cut tube of this invention.
Chronic total occlusion (CTO) remains one of the most challenging pathologies encountered by surgeons and interventionalists alike. CTO is characterized by heavy atherosclerotic plaque burden resulting in complete, or near complete occlusion of a vessel for at least 1-3 months. CTO can occur in any part of the arterial vasculature, however, it is most common in the legs and other arteries near the heart. Chronic occlusions are present in up to 40% of patients who undergo treatment of symptomatic peripheral artery disease (PAD) and have been cited as one of the primary reasons for procedural failures. PAD is a prevalent condition, affecting about 10 million individuals in the United States and over 27 million individuals worldwide. CTO is also prolific in patients with coronary artery disease (CAD), the number one cause of death in the U.S. in both men and women, killing over 400,000 each year. Approximately 30% of all coronary angiograms in patients with coronary artery disease will show a CTO.
Restoring blood flow to the affected area is essential for improving blood supply and tissue perfusion to prevent limb amputation, heart failure and other clinical symptoms associated with these diseases. There are presently two predominate treatment strategies for CTO: bypass surgery or percutaneous recanalization. Until recently, CTOs of the coronary arteries were almost entirely referred for coronary artery bypass graft (CABG) procedures, or many were left untreated because of the high risk and uncertainty regarding CABG success rates. With a failure rate of up to 30%, recanalization poses its own set of technical challenges. A tough, fibrous cap is often present at the proximal and distal ends of the CTO with softer material in between. The majority of recanalization failures are due to an inability to cross the occlusion with the guidewire and balloon technologies currently available. Despite these challenges percutaneous revascularization has been associated with reduced angina, improved left ventricular function, reduced arrhythmias, and reduced mortality. Further innovations and refinement of current crossing catheter technologies are essential to increase procedural success in crossing long, calcified CTOs. Although the worst case for crossing a blocked vessel may be crossing one with a CTO, the intent of the invention is also for use for partial occlusions or simply crossing tortuous anatomy since the given construction can enable optimal performance in many applications.